Hydrogeological Field Guide to the Wessex Basin Technical Report IR/00/77 R Tyler-Whittle, P Shand, K J Griffiths and W M Edmunds This page is blank BRITISH GEOLOGICAL SURVEY Natural Environment Research Council TECHNICAL REPORT IR/00/77 Hydrogeology Series Technical Report IR/00/77 Hydrogeological Field Guide to the Wessex Basin R Tyler-Whittle, P Shand, K J Griffiths and W M Edmunds This report was prepared for an EU BASELINE fieldtrip. Bibliographic Reference Tyler-Whittle R, Shand P, Griffiths K J and Edmunds W M, 2000 Hydrogeological Field Guide to the Wessex Basin British Geological Survey Report IR/00/77 NERC copyright 2000 British Geological Survey Keyworth, Nottinghamshire BRITISH GEOLOGICAL SURVEY BRITISH GEOLOGICAL SURVEY KEYWORTH NOTTINGHAM NG12 5GG UNITED KINGDOM TEL (0115) 9363100 FAX (0115) 9363200 DOCUMENT TITLE AND AUTHOR LIST Hydrogeological Field Guide to the Wessex Basin R Tyler-Whittle, P Shand, K J Griffiths and W M Edmunds CLIENT CLIENT REPORT # BGS REPORT# IR/00/77 CLIENT CONTRACT REF BGS PROJECT CODE CLASSIFICATION Restricted SIGNATURE DATE SIGNATURE DATE PREPARED BY CO-AUTHOR (Lead Author) CO-AUTHOR CO-AUTHOR PEER REVIEWED BY CO-AUTHOR CHECKED BY CO-AUTHOR (Project Manager or deputy) CO-AUTHOR APPROVED BY CO-AUTHOR (Project Director or senior staff) CO-AUTHOR APPROVED BY OS Copyright (Hydrogeology acknowledged Group Manager) Assistant Director Layout checked by clearance (if reqd) BRITISH GEOLOGICAL SURVEY The full range of Survey publications is available from Keyworth, Nottingham NG12 5GG the BGS Sales Desk at the Survey headquarters, ☎ 0115-936 3100 Telex 378173 BGSKEY G Keyworth, Nottingham. The more popular maps and Fax 0115-936 3200 books may be purchased from BGS-approved stockists Murchison House, West Mains Road, Edinburgh, EH9 3LA and agents and over the counter at the Bookshop, Gallery ☎ 37, Natural History Museum, Cromwell Road, (Earth 0131-667 1000 Telex 727343 SEISED G Fax 0131-668 2683 Galleries), London. Sales Desks are also located at the BGS London Information Office, and at Murchison London Information Office at the Natural History Museum, House, Edinburgh. The London Information Office Earth Galleries, Exhibition Road, South Kensington, London maintains a reference collection of BGS publications SW7 2DE including maps for consultation. Some BGS books and ☎ 0171-589 4090 Fax 0171-584 8270 reports may also be obtained from HMSO Publications ☎ 0171-938 9056/57 Centre or from HMSO bookshops and agents. St Just, 30 Pennsylvania Road, Exeter EX4 6BX The Survey publishes an annual catalogue of maps, ☎ 01392-78312 Fax 01392-437505 which lists published material and contains index maps for several of the BGS series. Geological Survey of Northern Ireland, 20 College Gardens, Belfast BT9 6BS ☎ 01232-666595 Fax 01232-662835 The British Geological Survey carries out the geological Maclean Building, Crowmarsh Gifford, Wallingford, survey of Great Britain and Northern Ireland (the latter Oxfordshire OX10 8BB as an agency service for the government of Northern ☎ 01491-838800 Fax 01491-692345 Ireland), and of the surrounding continental shelf, as well as its basic research projects. It also undertakes programmes of British technical aid in geology in developing countries as arranged by the Department for Parent Body International Development. Natural Environment Research Council Polaris House, North Star Avenue, Swindon, Wiltshire SN2 1EU The British Geological Survey is a component body of the ☎ Natural Environment Research Council. 01793-411500 Telex 444293 ENVRE G Fax 01793-411501 Contents 1. ITINERARY: SUNDAY 14 MAY 2000 1 2. INTRODUCTION TO THE WESSEX BASIN 5 2.1 Geology 5 2.2 Hydrogeology 5 2.3 Groundwater Quality 8 2.4 Palaeowaters in the Wessex Basin 11 3. THE FIELD GUIDE 12 3.1 Stop 1: Bourne Catchment 12 3.2 Stop 2: ASR Site, Lytchett Minster, Wessex Water 15 3.3 Stop 3: The South Dorset Coast 19 4. OTHER FEATURES OF INTEREST 29 4.1 Oil Reserves in the Wessex Basin 29 4.2 Geothermal Energy 33 REFERENCES 36 ACKNOWLEDGEMENTS 37 i List of Figures Figure 2 The distribution of solution features in the Chalk of the Dorset Heathlands (from Allen et al., 1997). 3 Figure 3 Geological sketch map of the Wessex Basin, showing principal structures (from Chatwin, 1960) 6 Figure 4 Location map of the Chalk of south Dorset, illustrating the Chalk outcrop and the river network (from Allen et al., 1997). 8 Figure 6 Trilinear plot of groundwaters in the Wessex Water area (from Edmunds, 1996). 10 Figure 7 River Bourne at Cholderton on 2 February 2000 (upper) and 6 May 2000 (lower) following heavy April rainfall. 13 Figure 9 Original abstraction borehole at Lytchett Minster. 15 Figure 10 Schematic section at Lytchett Minster showing location of depth sampling tubes and main inflow horizons in the ASR Well (modified from Williams et al., 1999). 16 Figure 11 Dual porosity effects illustrated for each stage of an ASR cycle (from Gaus et. al. 2000). 17 Figure 12 Lytchett Minster Injection-recovery phase 1: Percent mixing calculated for different solutes against percent water recovered. 18 Figure 13 Structural setting of the south Dorset coast showing the control exerted by the Weymouth and Purbeck anticlines (after Donovan and Stride, 1961), in Goudie and Brunsden, 1997. 19 Figure 14 Cross section from the Winterbourne Kingston Borehole (north-west) through the Isle of Purbeck (south-east) [see Figure 1 for locations] (IGS and Wessex Water Authority, 1979). 20 Figure 15 Aerial view eastwards from Durdle Door to Kimmeridge Bay (from BGS, 1995). 21 Figure 16 View of the Durdle Door viewpoint looking south west over Durdle Cove. 22 Figure 17 The basal pebble bed of the Gault. 22 Figure 18 The Dorset coast between Man-O’-War Head and Bat’s Head showing features of geological interest (from House 1993). 23 Figure 19 Geological sketch map of the Lulworth district (from House 1993). 24 Figure 20 Geological cross section north-south through Lulworth Cove, indicating the location of the Lulworth borehole (from House, 1993). 25 Figure 21 The Lulworth Crumple at Stair Hole. 25 Figure 22 Contours on the surface on the water table for December 1982 (from Houston et al., 1986). 26 Figure 23 Lulworth groundwater investigation (from IGS and Wessex Water Authority, 1979). 27 Figure 24 Stages in the postulated evolution of the groundwater flow regime [groundwater divides marked by lines of circles] (from Houston et al., 1986). 28 Figure 25 (a) Interstitial water profiles and (b) recent geophysical logs for the Lulworth borehole (Edmunds et al., 2001). 29 Figure 26 Sections illustrating the geological evolution of the structure of the Wytch Farm Oilfield: Above; present day. Below; Tertiary, before alpine earth movements (from Colter and Harvard, 1981). 30 Figure 27 The Purbeck Fault and the Genesis of the Mupe Bay Palaeoseep (from Stoneley, 1982) 31 Figure 28 A correlation between Winterbourne Kingston and adjacent deep boreholes (after Rhys et al., 1982). 32 Figure 29 Bromide v. chloride in formation waters of the UK in relation to sea water: Mesozoic basins (from Edmunds, 1996b). 33 Figure 30 Salinity of groundwater in the Sherwood Sandstone Group in the Wessex Basin [grams/litre] (after Downing and Gray, 1986). 35 ii List of Tables Table 1 Geological succession in the Wessex Basin. 7 Table 2 Isotopic and chemical data for the Chalk groundwaters (depth profiles) in the Wessex Basin area. 11 Table 3 Geothermal Fluids from the Wessex Basin: Comparison of water from the Western Esplanade and Marchwood Wells (Southampton Area). 33 iii Introduction This report was produced as an itinerary for a European fieldtrip. The fieldtrip provided the introduction to a major programme of research into the Baseline water quality of European aquifers. Delegates from 10 countries attended the fieldtrip and this report was intended not only to provide details on the area, within the itinerary, but also to provide further information on the geology and hydrogeology of the Wessex Basin for future reference within the project. iv 1. ITINERARY: SUNDAY 14 MAY 2000 This itinerary was used for the BASELINE European party field trip on Sunday 14 May 2000 and therefore this section is intended to provide a brief overview of the day. Further details on each item are given in section 3 and are referenced here in italics. The route is illustrated in Figure 1 and approximate times of arrival are listed in brackets (i.e.: [10.00]). 1. The River Bourne [10.00] Our route from Abingdon towards the south coast crosses both the London Basin and the Wessex Basin. The southern limb of the London Basin can be seen as we drive south of Newbury, where the road cuts through the chalk escarpment. However, this fieldtrip will focus on the Wessex Basin. At Cholderton (home to the smallest water company in the UK), we turn south off the A303 to follow the River Bourne. The river runs mainly to the left of the road and demonstrates intermittent flow along its course and throughout the year. The Bourne forms the basis of a new research project for the BGS and the Environment Agency and there will be a chance to leave the bus and walk along a short stretch of the river (Section 3: STOP 1). 2. Salisbury Continuing south, we drive around Salisbury whose cathedral forms a landmark with the highest spire in England. Salisbury also forms the junction of four major rivers: River Avon, River Bourne, River Wylye and River Nadder. Leaving Salisbury, we continue to follow the River Bourne until Ringwood. Along this section we cross over from the gently dipping Chalk onto the Palaeogene. The western boundary of the New Forest follows the route, on our left, until we reach the A31 and travel west. 3. Aquifer Storage Recovery (ASR) [11.10] Arrive at Lytchett Minster, where Paul Stanfield from Wessex Water will explain the ASR programme (Section 3: STOP 2).